half frame qualifications

Among my souveniers I found a Vivitar plastic camera (35mm) which came as a gift for subscribing to Readers Digest or whatever. I notice it has a 25mm lens and that would be a perfect half frame lens. Everything is plastic (dunno abt. the lens) and I am tempted to crack it open to see if the winder could be modified to wind 4 teeth instead of eight of the sprocket wheel per single frame wind. Wouldn't it be a hoot if one could make a half frame onesself? :-).